Women may require more oxygen uptake than men for same fitness task

If you set a healthy man and a healthy woman in a room, put them on stationary bikes with an identical amount of resistance, and ask them to exercise for the same amount of time, the woman’s respiratory muscles will demand more oxygen to complete the task. That’s what a new study published Tuesday in The Journal of Physiology concludes, and the findings may suggest a sex-based difference in the way oxygen is processed in the human body.

Previous research has indicated that women’s airways are narrower than men’s— even between two people with lungs of equal size— and, thus, that moving the same amount of oxygen through these channels costs more for women than for men, study author William Sheel, kinesiology professor at the University of British Columbia, told FoxNews.com.

After considering that research, Sheel and his colleagues hypothesized that females’ respiratory muscles, such as the diaphragm and muscles surrounding the ribcage, would consume a greater amount of oxygen than men’s.

Over a course of four days, researchers had nine healthy adult women and nine healthy adult men complete about 500 experimental exercises to test how hard their respiratory muscles had to work, and how much oxygen they were using, to finish the same physical exercises.

Study authors placed a balloon in each person’s esophagus and stomach, and had them complete incremental exercises on a stationary bike. They measured the study participants’ ventilation and whole-body oxygen consumption at submaximal and maximal levels. Those levels fluctuated throughout the tests. At the lowest level, the exercise equated to riding a bike on a flat sidewalk and at the highest level simulated riding a bike as fast as possible at a steep incline.

Study participants then mimicked the breathing patterns associated with their incremental exercises while sitting on the bikes but not exercising. Researchers measured how much oxygen their respiratory muscles consumed, and they compared these levels to the amount the participants took in during physical exercise.

Despite a linear relationship between increased breathing and the respiratory muscles’ oxygen uptake among the men and women, the efficiency of these muscles was significantly lower in women. That discrepancy was most pronounced at maximal exercise, the researchers wrote in their paper.

Sheel said these findings have the potential to affect treatment for cardiorespiratory disease, as greater oxygen cost coupled with less efficient respiratory muscles could lead to a higher energy demand in women.

“If we prescribe an exercise or pulmonary rehab program at a given intensity— say, if we tell someone to exercise three times a week— should that be the same for men and women?” he told FoxNews.com.

Sheel noted that further study needs to be done on whether these sex-based differences may affect blood flow and distribution in the body. Previous research shows that men can exercise longer than women even when they use a ventilator, a device that eliminates the labor usually done by the respiratory muscles.

The findings may also have an impact on diagnoses and treatment of lung disease in women, Sheel pointed out.

“We need to describe and understand this in a healthy person before we start extrapolating to a disease population, but it’s starting to become a part of our thinking process,” Sheel said.